Display pixels with improved storage capacitance

ABSTRACT

A display may include one or more display pixels in an array of pixels. A display pixel may include a storage capacitor chat stores a pixel data signal. The storage capacitor may be formed from a pixel electrode structure, a capacitor electrode structure, and a common electrode structure that is interposed between the pixel electrode structure and capacitor electrode structures. Each electrode structure may be formed from transparent conductive materials deposited on respective display layers. The pixel electrode structure and capacitor electrode structure may be electrically coupled by a conductive via structure that extends through the display layers without contacting the common electrode structure. The conductive via structure may contact underlying transistor structures such as a source-drain structure.

This application claims the benefit of provisional patent applicationNo. 61/818,235, filed May 1, 2013, which is hereby incorporated byreference herein in its entirety.

BACKGROUND

This relates generally to electronic devices, and more particularly, toelectronic devices with displays.

Electronic devices often include displays. For example, cellulartelephones and portable computers often include displays for presentinginformation to a user.

It can be challenging to form displays for electronic devices. Displayssuch as liquid crystal displays typically include an array of pixels.Each pixel receives a data signal that is used by the pixel to displayimage information during display frames. The pixel includes a storagecapacitor that stores the data signal during each display frame. Thestorage capacitor is typically formed between pixel electrodes thatcontrol a layer of liquid crystal and a common electrode. In somescenarios such as for twisted-nematic (TN) displays, a common electrodeis formed on a color filter substrate (e.g., glass), whereas the pixelelectrode is formed over an additional common electrode formed on athin-film transistor substrate (e.g., glass). The color filter substratecovers the thin-film transistor substrate. For displays such as in-planeswitching (IPS) displays or fringe field switching (FFS) displays,display layers are typically formed over a single display substrate(e.g., glass). With ever-increasing display resolution, the availablearea for pixel electrodes is reduced, which constrains the maximumcapacitance between the pixel electrodes and the common electrode andpotentially results in insufficient storage capacitance and displayperformance shortcomings.

It would therefore be desirable to be able to provide improved displaysfor electronic devices.

SUMMARY

A display may include one or more display pixels in an array of pixels.A display pixel may include transistor structures that receive a pixeldata signal. The display pixel may include a storage capacitor thatstores the pixel data signal. The storage capacitor may be formed from apixel electrode structure, a capacitor electrode structure, and a commonelectrode structure that is interposed between the pixel electrodestructure and capacitor electrode structures. Each electrode structuremay be formed from transparent conductive materials deposited onrespective display layers such as passivation or organic layers. Thepixel electrode structure may use the pixel data signal to control aliquid crystal layer that covers the pixel electrode structure. Thepixel electrode structure and capacitor electrode structure may beelectrically coupled by a conductive via structure that extends throughthe display layers without contacting the common electrode structure.The conductive via structure may contact underlying transistorstructures such as a source-drain structure.

Further features of the invention, its nature and various advantageswill be more apparent from the accompanying drawings and the followingdetailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an illustrative electronic device suchas a laptop computer with a display in accordance with an embodiment ofthe present invention.

FIG. 2 is a perspective view of an illustrative electronic device suchas a handheld electronic device with a display in accordance with anembodiment of the present invention.

FIG. 3 is a perspective view of an illustrative electronic device suchas a tablet computer with a display in accordance with an embodiment ofthe present invention.

FIG. 4 is a perspective view of an illustrative electronic device suchas a computer display with display structures in accordance with anembodiment of the present invention.

FIG. 5 is a cross-sectional side view of an illustrative display inaccordance with an embodiment of the present invention.

FIG. 6 is a cop view of an illustrative array of display pixels in adisplay in accordance with an embodiment of the present invention.

FIG. 7 is a top view of an illustrative display pixel having pixelfinger structures and increased storage capacitance in accordance withan embodiment of the present invention.

FIG. 8 is a cross-sectional view of an illustrative display pixel havingpixel finger structures and increased storage capacitance in accordancewith an embodiment of the present invention.

FIG. 9 is a timing diagram showing how a display pixel having Increasedstorage capacitance may reduce leakage effects in accordance with anembodiment of the present invention.

FIG. 10 is a diagram of illustrative fabrication tools that may be usedto manufacture a display having display pixels with increased storagecapacitance in accordance with an embodiment of the present invention.

FIGS. 11A-11C show a flow diagram of illustrative steps that may beperformed using fabrication tools to manufacture a display havingdisplay pixels with increased storage capacitance in accordance with anembodiment of the present invention.

FIGS. 12A and 12B show a flow diagram of illustrative steps that may beperformed using fabrication tools to manufacture a display havingdisplay pixels with increased storage capacitance using a reduced numberof masks in accordance with an embodiment of the present invention.

FIGS. 13A-13D show a flow diagram of illustrative steps that may beperformed using fabrication tools to manufacture a display havingdisplay pixels with polysilicon transistor structures and increasedstorage capacitance in accordance with an embodiment of the presentinvention.

FIG. 14 is an illustrative cross-sectional diagram of a portion of adisplay having multiple common electrode layers and a pixel electrodeinterposed between the common electrode layers in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION

Electronic devices may include displays. The displays may be used todisplay images to a user. Illustrative electronic devices that may beprovided with displays are shown in FIGS. 1, 2, 3, and 4.

FIG. 1 shows how electronic device 10 may have the shape of a laptopcomputer having upper housing 12A and lower housing 12B with componentssuch as keyboard 16 and touchpad 18. Device 10 may have hinge structures20 that allow upper housing 12A to rotate in directions 22 aboutrotational axis 24 relative to lower housing 12B. Display 14 may bemounted in upper housing 12A. Upper housing 12A, which may sometimesreferred to as a display housing or lid, may be placed in a closedposition by rotating upper housing 12A towards lower housing 12B aboutrotational axis 24.

FIG. 2 shows now electronic device 10 may be a handheld device such as acellular telephone, music player, gaming device, navigation unit, orother compact device. In this type of configuration for device 10,housing 12 may have opposing front and rear surfaces. Display 14 may bemounted on a front face of housing 12. Display 14 may, if desired, haveopenings for components such as button 26. Openings may also be formedin display 14 to accommodate a speaker port (see, e.g., speaker port 28of FIG. 2).

FIG. 3 shows how electronic device 10 may be a tablet computer. Inelectronic device 10 of FIG. 3, housing 12 may have opposing planarfront and rear surfaces. Display 14 may be mounted on the front surfaceof housing 12. As shown in FIG. 3, display 14 may have an opening toaccommodate button 26 (as an example).

FIG. 4 shows how electronic device 10 may be a computer display or acomputer that has been integrated into a computer display. With thistype of arrangement, housing 12 for device 10 may be mounted on asupport structure such as stand 27. Display 14 may be mounted on a frontface of housing 12.

The illustrative configurations for device 10 that are shown in FIGS. 1,2, 3, and 4 are merely illustrative. In general, electronic device 10may be a laptop computer, a computer monitor containing an embeddedcomputer, a tablet computer, a cellular telephone, a media player, orother handheld or portable electronic device, a smaller device such as awrist-watch device, a pendant device, a headphone or earpiece device, orother wearable or miniature device, a television, a computer displaythat does not contain an embedded computer, a gaming device, anavigation device, an embedded system such as a system in whichelectronic equipment with a display is mounted in a kiosk or automobile,equipment that implements the functionality of two or more of thesedevices, or other electronic equipment.

Housing 12 of device 10, which is sometimes referred to as a case, maybe formed of materials such as plastic, glass, ceramics, carbon-fibercomposites and other fiber-based composites, metal (e.g., machinedaluminum, stainless steel, or other metals), other materials, or acombination of these materials. Device 10 may foe formed using a unibodyconstruction in which most or all of housing 12 is formed from a singlestructural element (e.g., a piece of machined metal or a piece of moldedplastic) or may be formed from multiple housing structures (e.g., outerhousing structures that have been mounted to internal frame elements orother internal housing structures).

Display 14 may be a touch sensitive display that includes a touch sensoror may be insensitive to touch. Touch sensors for display 14 may beformed from an array of capacitive touch sensor electrodes, a resistivetouch array, touch sensor structures based on acoustic touch, opticaltouch, or force-based touch technologies, or other suitable touch sensorcomponents.

Display 14 for device 10 includes display pixels formed from liquidcrystal display (LCD) components or other suitable image pixelstructures.

A display cover layer may cover the surface of display 14 or a displaylayer such as a color filter layer or other portion of a display may beused as the outermost (or nearly outermost) layer in display 14. Theoutermost display layer may foe formed from a transparent glass sheet, aclear plastic layer, or other transparent member.

A cross-sectional side view of an illustrative configuration for display14 of device 10 (e.g., for display 14 of the devices of FIG. 1, FIG. 2,FIG. 3, FIG. 4 or other suitable electronic devices) is shown in FIG. 5.As shown in FIG. 5, display 14 may include backlight structures such asbacklight unit 42 for producing backlight 44. During operation,backlight 44 travels outwards (vertically upwards in dimension Z In theorientation of FIG. 5) and passes through display pixel structures indisplay layers 46. This illuminates any images that are being producedby the display pixels for viewing by a user. For example, backlight 44may illuminate images on display layers 46 that are being viewed byviewer 48 in direction 50.

Display layers 46 may be mounted in chassis structures such as a plasticchassis structure and/or a metal chassis structure to form a displaymodule for mounting in housing 12 or display layers 46 may be mounteddirectly in housing 12 (e.g., by stacking display layers 46 into arecessed portion in housing 12). Display layers 46 may form a liquidcrystal display or may be used in forming displays of other types.

In a configuration in which display layers 46 are used in forming aliquid crystal display, display layers 46 may include a liquid crystallayer such a liquid crystal layer 52. Liquid crystal layer 52 may besandwiched between display layers such as display layers 58 and 56.Layers 56 and 58 may be interposed between lower polarizer layer 60 andupper polarizer layer 54.

Layers 58 and 56 may be formed from transparent substrate layers such asclear layers of glass or plastic. Layers 56 and 58 may be layers such asa thin-film transistor layer and/or a color filter layer. Conductivetraces, color filter elements, transistors, and other circuits andstructures may be formed on the substrates of layers 58 and 56 (e.g., toform a thin-film transistor layer and/or a color filter layer). Touchsensor electrodes may also be incorporated into layers such as layers 58and 56 and/or touch sensor electrodes may be formed on other substrates.

With one illustrative configuration, layer 58 may be a thin-filmtransistor layer that includes an array of thin-film transistors andassociated electrodes (display pixel electrodes) for applying electricfields to liquid crystal layer 52 and thereby displaying images ondisplay 14. Layer 56 may be a color filter layer that includes an arrayof color filter elements for providing display 14 with the ability todisplay color images. If desired, layer 58 may be a color filter layerand layer 56 may be a thin-film transistor layer.

During operation of display 14 in device 10, control circuitry (e.g.,one or more integrated circuits such as components 68 on printed circuit66 of FIG. 5) may be used to generate information to be displayed ondisplay 14 (e.g., display data). The information to be displayed may beconveyed from circuitry 68 to display driver integrated circuit 62 usinga signal path such as a signal path formed from conductive metal tracesin flexible printed circuit 64 (as an example).

Display driver integrated circuit 52 may be mounted onthin-film-transistor layer driver ledge 82 or elsewhere in device 10. Aflexible printed circuit cable such as flexible printed circuit 64 maybe used in routing signals between printed circuit 66 andthin-film-transistor layer 58. If desired, display driver integratedcircuit 62 may be mounted on printed circuit 66 or flexible printedcircuit 64. Printed circuit 66 may be formed from, a rigid printedcircuit board (e.g., a layer of fiberglass-filled epoxy) or a flexibleprinted circuit (e.g., a flexible sheet of polyimide or other flexiblepolymer layer).

Backlight structures 42 may include a light guide plate such as lightguide plate 78. Light guide plate 78 may be formed from a transparentmaterial such as clear glass or plastic. During operation of backlightstructures 42, a light source such as light source 72 may generate light74. Light source 72 may be, for example, an array of light-emittingdiodes.

Light 74 from light source 72 may be coupled into edge surface 76 oflight guide plate 78 and may be distributed in dimensions X and Ythroughout light guide plate 78 due to the principal of total internalreflection. Light guide plate 78 may include light-scattering featuressuch as pits or bumps. The light-scattering features may be located onan upper surface and/or on an opposing lower surface of light guideplate 78.

Light 74 that scatters upwards in direction Z from light guide plate 78may serve as backlight 44 for display 14. Light 74 that scattersdownwards may be reflected back in the upwards direction by reflector80. Reflector 80 may be formed from a reflective material such as alayer of white plastic or other shiny materials.

To enhance backlight performance for backlight structures 42, backlightstructures 42 may include optical films 70. Optical films 70 may includediffuser layers for helping to homogenize backlight 44 and therebyreduce hotspots, compensation films for enhancing off-axis viewing, andbrightness enhancement films (also sometimes referred to as turningfilms) for collimating backlight 44. Optical films 70 may overlap theother structures in backlight unit 42 such as light guide plate 78 andreflector 80. For example, if light guide plate 78 has a rectangularfootprint in the X-Y plane of FIG. 5, optical films 70 and reflector 80may have a matching rectangular footprint.

As shown in FIG. 6, display 14 may include a pixel array such as pixelarray 92. Pixel array 92 may be controlled using control signalsproduced by display driver circuitry. Display driver circuitry may beimplemented using one or more integrated circuits (ICs) and maysometimes be referred to as a driver IC, display driver integratedcircuit, or display driver.

During operation of device 10, control circuitry in device 10 such asmemory circuits, microprocessors, and other storage and processingcircuitry may provide data to the display driver circuitry. The displaydriver circuitry may convert the data into signals for controlling thepixels of pixel array 92.

Pixel array 92 may contain rows and columns of display pixels 90. Thecircuitry of pixel array 92 may be controlled using signals such as dataline signals on data lines D and gate line signals on gate lines G.

Pixels 90 in pixel array 92 may contain thin-film transistor circuitry(e.g., polysilicon transistor circuitry, indium gallium zinc oxidetransistor circuitry, or amorphous silicon transistor circuitry) andassociated structures for producing electric fields across liquidcrystal layer 52 in display 14. Each display pixel may have a respectivethin-film transistor such as thin-film transistor 94 to control theapplication of electric fields to a respective pixel-sized portion 52′of liquid crystal layer 52.

The thin-film transistor structures that are used in forming pixels 90may be located on a thin-film transistor substrate such as a layer ofglass. The thin-film transistor substrate and the structures of displaypixels 90 that are formed on the surface of the thin-film transistorsubstrate collectively form thin-film transistor layer 58 (FIG. 5).

Gate driver circuitry may be used to generate gate signals on gate linesG. The gate driver circuitry may be formed from thin-film transistors onthe thin-film transistor layer or may be implemented in separateintegrated circuits. Gate driver circuitry may be located on both theleft and right sides of pixel array 92 or on one side of pixel array 92(as examples).

The data line signals on data lines D in pixel array 92 carry analogimage data (e.g., voltages with magnitudes representing pixel brightnesslevels). During the process of displaying images on display 14, adisplay driver integrated circuit may receive digital data from controlcircuitry and may produce corresponding analog data signals. The analogdata signals may be demultiplexed and provided to data lines D.

The data line signals on data lines D are distributed to the columns ofdisplay pixels 90 in pixel array 92. Gate line signals on gate lines Gare provided to the rows of pixels 90 in pixel array 92 by associatedgate driver circuitry.

The circuitry of display 14 such as demultiplexer circuitry, gate drivercircuitry, and the circuitry of pixels 90 may be formed from conductivestructures (e.g., metal lines and/or structures formed from transparentconductive materials such as indium tin oxide) and may includetransistors such as transistor 94 that are fabricated on the thin-filmtransistor substrate layer of display 14. The thin-film transistors maybe, for example, polysilicon thin-film transistors or amorphous silicontransistors.

As shown in FIG. 6, pixels such as pixel 90 may be located at theIntersection of each gate line G and data line D in array 92. A datasignal on each data line D may foe supplied to terminal 96 from one ofdata lines D. Thin-film transistor 94 (e.g., a thin-film polysilicontransistor or an amorphous silicon transistor) may have a gats terminalsuch as gate 98 that receives gate line control signals on gate linesignal path G. When a gate line control signal is asserted, transistor94 will be turned on and the data signal at terminal 96 will be passedto node 100 as voltage Vp. Data for display 14 may be displayed inframes. Following assertion of the gate line signal in each row to passdata signals to the pixels of that row, the gate line signal may bedeasserted. In a subsequent display frame, the gate line signal for eachrow may again be asserted to turn on transistor 94 and capture newvalues of Vp.

Pixel 90 may nave a signal storage element such as a capacitor havingcapacitance C_(ST) or other charge storage element. The storagecapacitor may be used to store signal Vp in pixel 90 during and/orbetween frames (e.g., in the period of time between the assertion ofsuccessive gate signals).

Display 14 may have a common electrode coupled to node 104. The commonelectrode (which is sometimes referred to as the Vcom electrode) may beused to distribute a common electrode voltage such as common electrodevoltage Vcom to nodes such as node 104 in each pixel 90 of array 92. Asshown by illustrative electrode pattern 104′ of FIG. 6, Vcom electrode104 may be implemented using a blanket film of a transparent conductivematerial such as indium tin oxide (e.g., electrode 104 may be formedfrom, a layer of indium tin oxide that covers substantially all ofpixels 90 in array 92). If desired, electrode 104 may be partitionedinto separate portions that each covers a respective group of pixels 90in array 92.

In each pixel 90, capacitance C_(ST) may be formed between nodes 100 and104. A parallel capacitance arises across nodes 100 and 104 due toelectrode structures in pixel 90 that are used in controlling theelectric field through the liquid crystal material of the pixel (liquidcrystal material 52′). As shown in FIG. 6, electrode structures 106 maybe coupled to node 100. Capacitance C_(LC) across liquid crystalmaterial 52′ is associated with the capacitance between electrodestructures 106 and common electrode Vcom at node 104. During operation,electrode structures 106 may be used to apply a controlled electricfield (i.e., a field having a magnitude proportional to Vp-Vcom) acrosspixel-sized liquid crystal material 52′ in pixel 90. Due to the presenceof storage capacitance C_(ST) and capacitance C_(LC) across liquidcrystal material 52′, the value of Vp (and therefore the associatedelectric field across liquid crystal material 52′) may be maintainedacross nodes 106 and 104 for the duration of the frame.

The electric field that is produced across liquid crystal material 52′causes a change in the orientations of the liquid crystals in liquidcrystal material 52′. This changes the polarization of light passingthrough liquid crystal material 52′. The change in polarization may, inconjunction with polarizers 60 and 54 of FIG. 4, be used in controllingthe amount of light 44 that is transmitted through each pixel 90 inarray 92 of display 14.

As shown in FIG. 7, pixel 90 may include electrode structures 106-1 and106-2 that are formed in parallel. The electrode structures may havelengths that extend substantially across the pixel (e.g., the activearea of the pixel through which light is emitted) and may sometimes bereferred to as electrode fingers or pixel fingers. Each pixel finger mayhave a width W and may be separated from an adjacent pixel finger bydistance D. For example, pixel finger 106-1 may be separated fromadjacent pixel finger 106-2 by distance D. Width W may be about 3 μm,whereas distance D may be about 5 μm (as examples). Width W and distanceD may be determined so that pixel fingers 106 form desired field linesto underlying common electrode Vcom. For example, the ratio betweenwidth W and distance D may be required to be greater than or equal to athreshold value (e.g., a ratio of 3 μm to 5 μm).

The storage capacitance between electrodes 106 and underlying commonelectrode Vcom may be constrained by the area of pixel fingers 106. Asdisplay resolution increases, the pixel pitch F decreases. For example,at high display resolutions, the pixel pitch P may be 16 μm or less. Ata pixel pitch of 16 μm, only two pixel fingers 106 may be formed whilesatisfying minimum width-to-distance constraints. However, the area oftwo pixel fingers 106 may be insufficient to provide a desired amount ofcapacitance C_(ST). To provide an Increased amount of capacitanceC_(ST), an electrode layer 112 may be formed under common electrodeVcom. Electrode layer 112 may be electrically coupled (e.g., shorted) topixel fingers 106 by a conductive via structure 107 and serve toincrease the parallel plate capacitance that forms C_(ST). Electrodelayer 112 may have an area that is substantially the same as pixel 90 ormay have any desired area or shape. Conductive via structure 107 may beformed through an opening in the common electrode Vcom so that viastructure 107 electrically couples pixel electrode structures (e.g.,fingers 106) to electrode layer 112 without contacting common electrodeVcom.

FIG. 8 is an illustrative cross-sectional diagram of a portion of pixel90 having increased storage capacitance. As shown in FIG. 8, pixelfingers 122 may be separated from common electrode Vcom by passivationlayer 124 (e.g., silicon nitride or silicon oxide). During displayoperations, field lines 122 and 124 may be produced between pixelfingers (e.g., fingers 106-1 and 106-2) and common electrode Vcom. Fieldlines 122 may contribute to capacitance C_(LC) associated with liquidcrystal layer 52. Field lines 124 may contribute to storage capacitanceC_(ST) between fingers 106 and common electrode Vcom.

Pixel 90 may Include additional electrode layer 112 that is formed onorganic layer 128 underneath common electrode Vcom. During operation ofpixel 90, field lines 126 may be formed between electrode layer 112 andcommon electrode Vcom. Electrode layer 112 may effectively form aparallel plate capacitance with common electrode Vcom that is combinedwith the parallel plate capacitance between fingers 106 and commonelectrode Vcom to form storage capacitance C_(ST). Storage capacitanceC_(ST) may be adjusted to a desired value. For example, higher storagecapacitance may ensure that sufficient charge is held between displayframes, whereas lower storage capacitance may ensure that capacitancecharging during initial frame operations is sufficiently quick.

Storage capacitance C_(ST) may be determined from the area of fingers106 that overlaps common electrode Vcom, thickness T1 of passivationlayer 124, thickness T2 of passivation layer 126, the area of additionalelectrode layer 112 that overlaps common electrode Vcom, and thedielectric constant of passivation layers 124 and 126. Storagecapacitance C_(ST) may be reduced by reducing the area of fingers 106(e.g., reducing W or reducing the number of fingers), increasingthickness T1, increasing thickness T2, reducing the area of additionalelectrode layer 112, reducing the dielectric constant of layer 124,reducing the dielectric constant of layer 126, or any combination ofthese adjustments. Storage capacitance C_(ST) may be increased byincreasing the area of fingers 106 (e.g., increasing W or increasing thenumber of fingers), reducing thickness T1, reducing thickness T2,increasing the area of additional electrode layer 112, increasing thedielectric constant of layer 124, increasing the dielectric constant oflayer 126, or any combination of these adjustments.

The example of FIG. 8 in which the Vcom electrode is interposed betweenpixel electrodes and additional capacitor electrode 112 is merelyillustrative. If desired, the functions of pixel electrode structures106 and the Vcom electrode structure may be swapped. For example,electrode structures 106 may serve as Vcom electrode structures, whereasthe Vcom electrode structure as labeled in FIG. 8 may serve as pixelelectrode structures (e.g., provided with pixel signals).

FIG. 9 is an illustrative timing diagram of absolute pixel voltage overrime during display operations. At the start of each frame (e.g., frame1, frame 2, etc.), the pixel voltage may be set to a desired voltage.During each frame, the absolute pixel voltage may decrease due toleakage (e.g., transistor leakage). Solid line 132 may represent pixelvoltage for pixel 90 having additional electrode layer 112, whereasdashed line 134 may represent pixel voltage for a pixel withoutadditional electrode layer 112. As shown by solid line 132, the pixelvoltage of pixel 90 may be maintained at higher levels than the pixelvoltage associated with dashed line 134 (e.g., voltage drop due toleakage may be reduced).

FIG. 10 is a diagram of illustrative fabrication tools 142 that may beused to manufacture a display with pixels having increased storagecapacitance. As shown in FIG. 10, fabrication tools 142 may includedepositing tools 144, photolithography tools 146, and etching tools 143.Depositing tools 34 may include tools for sputtering, performing atomiclayer deposition (ALD), molecular beam epitaxy (MBE), electrochemicaldeposition (ECD), chemical vapor deposition (CVD), physical vapordeposition (PVD), ion implantation tools, etc. Depositing tools 34 maybe used to deposit conductive layers, dielectric layers, etch stoplayers, or other materials on a display substrate such as glass.Photolithography tools 128 may be used to apply one or more photoresistmasks 150 over the display substrate (e.g., to pattern one or morelayers of material on the display substrate). Masks 150 may, forexample, define regions of material that should be removed (e.g., usingetching tools 40) and regions of material that should be maintained.Etching tools 40 may, for example, include wet etching tools or dryetching tools. Etching tools 40 may be used to remove photoresistmaterial, conductive layers, dielectric layers, or other materials onthe display.

FIGS. 11A, 11B, and 11C show a diagram 200 of illustrative steps thatmay be performed using fabrication tools 142 to form a display withincreased storage capacitance. As shown in FIG. 11A, a display substrate212 may be provided at initial step 210. Display substrate 212 may be athin film transistor substrate such as glass.

During step 220, depositing tools 144 may be used to deposit a layer ofgate metal such as aluminum, other metals, metal alloys, or otherdesired conductive materials. The conductive materials may be opaque or,if desired, may be transparent. Photolithography tools 146 may be usedto apply a gate mask 224 that defines gate electrode 222. Excess gatemetal materials may be removed using etching tools 148 (e.g., gatemetals not covered by the gate mask).

During step 230, a dielectric layer 232 may be deposited usingdepositing tools 144 over gate electrode 222 and substrate 212. Asemiconductor layer such as amorphous silicon or indium gallium zincoxide may be deposited and patterned using a channel mask 234 to formchannel structure 234 (e.g., using depositing tools 144,photolithography tools 146, and etching tools 148).

During step 240, a passivation layer 242 may be deposited over channelstructures 234 and dielectric layer 232. Passivation layer 242 may be alayer of dielectric materials such as silicon nitrides or siliconoxides. A via hole mask 244 may be used to form via openings 246 thatextend through passivation layer 242.

During step 250, metal material such as aluminum or other materialssimilar to gate electrode 222 may be deposited over passivation layer242 and patterned using source-drain mask 252 to form source-drainstructures 254. The layer of metal may fill via holes 246 so thatsource-drain structures 254 are electrically coupled to and contactchannel structure 234.

During step 260, an organic layer 128 may be deposited over source-drainstructures 254. The organic layer may be formed from acrylics or otherorganic materials. Via hole 266 may be formed over source-drain contact254-1 in organic layer 128.

During step 270, a layer of conductive material may be deposited overorganic layer 128. The layer of conductive material may fill at least aportion of via hole 266 and may contact source-drain structure 254-1.The conductive material may be a transparent conductive material such asindium tin oxide (ITO) to pass light from underlying display backlightstructures. The layer of conductive material may be patterned using acapacitor electrode mask 272 to form storage capacitor electrode 112.Capacitor electrode mask 272 may define openings 274 between electrode112 and adjacent pixels so as to avoid electrical shorting betweenstorage capacitors of adjacent pixels.

During step 280, a passivation layer 282 may be deposited and a via holemask 284 may be used to form a via hole 285 in passivation layer 282(e.g., similar to via hole 266 formed in organic layer 128). Atransparent conductive layer similar to layer 112 may be subsequentlydeposited in opening 285 and over passivation layer 282. The transparentconductive layer may be patterned using Vcom mask 286 to form a commonelectrode Vcom (a first portion) and a second, via portion 288 that isseparated from the common electrode Vcom by gap 289. Gap 289 may help toensure that common electrode Vcom is electrically isolated fromtransistor structures such as source-drain structure 254-1. Portion 288of the transparent conductive layer contacts and is electrically coupledto capacitor electrode layer 112. Vcom mask 286 may additionally defineone or more gaps 281 that separate the conductive layer from adjacentpixels (e.g., electrically isolating the Vcom electrode and transistorstructures from adjacent pixels).

During step 290, a passivation layer 291 may be deposited and a via holemask 292 may be used to form via hole 293 in passivation layer 291(e.g., similar to via hole 266 and 285). A transparent conductive layer(e.g., a layer of ITO) may be subsequently deposited in opening 293 andover passivation layer 291. The transparent conductive layer may bepatterned using pixel finger mask 294 to form pixel fingers 106-1 and106-2 and a via portion 295. Via portion 295 may foe electricallyisolated from adjacent pixels by gap 296. Via portion 295 may beelectrically coupled to pixel fingers 106-1 and 106-2 (e.g., using metaltraces on other portions of passivation layer 291). Via portions 295 and288 electrically couple (e.g., short) pixel fingers to capacitorelectrode 112 without electrically shorting to common electrode Vcom.

If desired, one or more steps of flow diagram 200 may be omitted toreduce manufacturing complexity and cost. For example, one or more masksused in the steps of flow diagram 200 may be omitted. FIGS. 12A, 12B,and 12C show a flow diagram of illustrative steps that may be performedwith a reduced number of masks. Subsequent to formation of thin filmtransistor structures (e.g., by performing steps 210-250 of FIG. 11A),an optional protection layer 302 may be deposited over the thin filmtransistor structures and passivation layer 242. Optional protectionlayer 302 may be formed from similar materials used to form passivationlayers (e.g., silicon oxides, silicon nitrides, etc.). Layer 302 may beused to help protect underlying transistor structures from moisturedamage. If desired, optional protection layer 302 may be omitted.

During step 320, organic layer 128 may be deposited and via hole mask264 may be used to form via hole (opening) 266 in the organic layer(e.g., similar to step 260 of FIG. 11B). A layer of transparentconductive material may be deposited and patterned using capacitorelectrode mask 322 to form capacitor electrode 112. Capacitor electrodemask 322 may define capacitor electrode 112 so that electrode 112 doesnot extend over via hole 266 (e.g., mask 322 may expose via hole 266 sothat etching tools remove any portion of the transparent conductivelayer that is within via opening 266). The example of FIG. 12A is merelyillustrative. If desired, capacitor electrode mask 272 of FIG. 11B maybe used so that capacitor electrode 112 extends over via opening 266.

During step 330, passivation layer 282 may be deposited over capacitorelectrode 112 and organic layer 128. In the example of FIG. 12A, viahole mask 284 of step 280 of FIG. 11C may be omitted. A layer oftransparent conductive material may be subsequently deposited andpatterned using Vcom mask 332 to form common electrode Vcom. Vcom mask332 may define common electrode Vcom to leave regions over transistorstructures and underlying capacitor electrode 112 exposed. For example,edge 334 of common electrode Vcom may be separated from edge 336 ofcapacitor electrode 112 by distance X. By exposing regions overunderlying transistor structures and underlying capacitor electrode 112,Vcom mask 332 may ensure that subsequent via formation steps do notelectrically short common electrode Vcom to the transistor structures orthe capacitor electrode.

During step 340, passivation layer 341 may be deposited over commonelectrode Vcom and passivation layer 282. Via hole mask 342 may besubsequently used to form via opening 344 in passivation layers 341 and282. A single etching step may be used with via hole mask 342, becausepassivation layers 341 and 282 may be formed from the same or similarmaterials. Etching performed using etching tools with via hole mask 342may expose portion 345 of capacitor electrode 345 and transistorsource-drain structure 254-1.

During step 350, a layer of transparent conductive material may bedeposited and patterned using pixel finger mask 294 to form via portion352 and pixel electrodes 106-1 and 106-2 (e.g., similarly to step 290 ofFIG. 11C). Via portion 352 may contact, capacitor electrode 112 andsource-drain structure 254-1 (e.g., via portion 352 may electricallycouple pixel fingers, capacitor electrode 112, and source-drainstructure 254-1.

If desired, thin film transistor structures may be formed usingpolysilicon. FIGS. 13A, 13B, 13C, and 13D show a diagram 400 ofillustrative steps that may be performed using fabrication tools to forma display with polysilicon transistor structures and increased storagecapacitance.

During step 410, an optional opaque layer (e.g., opaque metal or otheropaque materials) may be deposited on substrate 212 and patterned usinglight shield mask 412 to form light shield structure 414, If desired,step 410 may be omitted.

During step 420, dielectric material 421 may be deposited over lightshield structure 414 and substrate 212. Semiconductor material such aspolysilicon may be deposited over dielectric material 421 and patternedusing channel mask 422 to form channel structure 424 (e.g., similar tochannel mask 234 of FIG. 11A). Polysilicon channel structures may besensitive to light emitted by underlying backlight structures. Channelstructure 424 formed from polysilicon may be covered by optional lightshield structure 414 to help protect the polysilicon channel structurefrom underlying backlight structures (e.g., by blocking light from thebacklight structures).

During step 430, a passivation layer 432 may be deposited over channelstructures 424. A layer of metal or other conductive materials may bedeposited over passivation layer 432 and subsequently patterned usinggate mask 434 to form gate structure 436. Gate structure 436 may controlcurrent, flow through channel 424 during display operation.

During step 440, a passivation layer 442 may be deposited overpassivation layer 432 and gate structures 436. A via hole mask 444 maybe subsequently used to form via holes 446 that extend throughpassivation layers 432 and 442 and expose portions of channel structure424.

During step 450, a layer of metal or other conductive material may bedeposited over passivation layer 442 and subsequently patterned usingsource-drain mask 452 to form source-drain structures 454 that extendthrough passivation layers 432 and 444 to contact channel structure 424.

As shown in FIG. 13C, step 460 may be subsequently performed usingfabrication tools to form a conductive via structure (e.g., portions 288and 295) that electrically couples capacitor electrode structure 112,pixel fingers 106, and source-drain structure 454-1. Step 460 may, forexample, include steps 260-290 of FIGS. 11B and 11C. If desired, one ormore masks may be omitted to reduce complexity and cost. In the exampleof FIG. 13D, light shield mask 412 and via hole mask 284 may be omitted.In other words, step 410 of FIG. 13B may be omitted and steps 320-350 ofFIGS. 12A and 12B may be performed subsequent to step 450 of FIG. 13B(e.g., a single via hole mask 342 may be used to form a via openingthrough passivation layers 341 and 282).

FIG. 14 is an illustrative cross-sectional diagram of a portion of adisplay in which pixel electrode structures may be interposed betweencommon electrode structures. As shown in FIG. 14, transistor structures(e.g., source-drain structures 454, gate structure 436, and channelstructure 424) may be formed on display substrate 212. This example ismerely illustrative. If desired, amorphous silicon transistorstructures, polysilicon transistor structures, or any desired transistorstructures may be formed on display substrate 212.

A capacitor electrode 112 may be formed similarly to FIG. 13D. Ifdesired, capacitor electrode structure 112 may be formed similarly toFIG. 13C. Pixel electrode structures 501 may be formed on passivationlayer 282. Via structure 502 may be formed through passivation layer 282and organic layer 128 to contact source-drain structure 454 withoutcontacting capacitor electrode structure 112. A passivation layer 341may be deposited over via structure 502 and passivation layer 282, Vcomelectrode structures may be formed over passivation layer 341 similarlyto pixel electrode structures of FIG. 13D (e.g., the Vcom electrodestructures may be patterned, to form fingers). Via structure 504 may beformed to extend through passivation layers 341 and 282 to electricallycouple Vcom electrode structures to capacitor electrode structure 112.In the example of FIG. 14, additional capacitance provided between pixelelectrode structures 501 and capacitor electrode 112 may provideincreased storage capacitance (e.g., in addition to storage capacitanceprovided between the Vcom electrode structures and pixel electrodestructures 501.

The foregoing is merely illustrative of the principles of this inventionand various modifications can be made by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A display, comprising: a pixel electrodestructure for a pixel; a capacitor electrode structure that iselectrically coupled to the pixel electrode structure, wherein thecapacitor electrode structure increases a storage capacitance of thepixel; a common electrode layer, wherein the common electrode layer hasa transparent portion and wherein the transparent portion is interposedbetween the pixel electrode structure and the capacitor electrodestructure; and a source-drain structure that is electrically coupled tothe capacitor electrode structure and the pixel electrode structure witha via structure that includes a portion of the pixel electrodestructure, wherein the portion of the pixel electrode structure in thevia structure overlaps the source-drain structure, and wherein thecapacitor electrode structure is interposed between the source-drainstructure and the pixel electrode structure.
 2. The display defined inclaim 1 wherein the display further comprises: a common electrodestructure in the common electrode layer; a display substrate; andtransistor structures that include the source-drain structure, whereinthe transistor structures are formed over the display substrate, andwherein the transistor structures are electrically coupled to thecapacitor electrode structure and the pixel electrode structure.
 3. Thedisplay defined in claim 2 wherein the capacitor electrode structure andthe pixel electrode structure form a storage capacitor with the commonelectrode structure.
 4. The display defined in claim 3 furthercomprising: an array of pixels, wherein the transistor structures andthe storage capacitor forms at least a portion of a pixel of the arrayof pixels.
 5. The display defined in claim 4 wherein the displaysubstrate comprises a glass substrate, wherein the source-drainstructure comprises a first source-drain structure, and wherein thetransistor structures further comprise: a second source-drain structure;a channel structure; and a gate structure.
 6. The display defined inclaim 5 further comprising: a data line that is coupled to the secondsource-drain structure, wherein the data line conveys a pixel datasignal to the second source-drain structure and wherein the storagecapacitor stores the pixel data signal.
 7. The display defined in claim6 further comprising a liquid crystal layer that covers the pixelelectrode structure.
 8. The display defined in claim 3 wherein the pixelelectrode structure comprises a plurality of pixel fingers arranged inparallel.
 9. The display defined in claim 3 wherein the via structureelectrically couples the source-drain structure, the capacitor electrodestructure, and the pixel electrode structure without contacting thecommon electrode structure.
 10. A display pixel that receives a pixeldata signal, the display pixel comprising: a common electrode, whereinthe common electrode comprises a transparent conductive material; apixel electrode that covers at least a portion of the common electrode,wherein the pixel electrode receives the pixel data signal, wherein thepixel electrode comprises a plurality of pixel fingers arranged inparallel; a conductive layer that is covered by the common electrode,wherein the conductive layer, the pixel electrode, and the commonelectrode form a storage capacitor that stores the pixel data signalduring display frames, wherein the conductive layer overlaps at leasttwo of the plurality of pixel fingers; a gate electrode, wherein theconductive layer is interposed between the gate electrode and the pixelelectrode a first passivation layer that covers the conductive layer,wherein the common electrode is formed on the first passivation layer; asecond passivation layer that covers the common electrode, wherein thepixel electrode is formed on the second passivation layer; and a viastructure that extends through the first and second passivation layers,wherein the via structure electrically couples the pixel electrode tothe conductive layer without contacting the common electrode, wherein aportion of the via structure is interposed between the first passivationlayer and the second passivation layer and separates the firstpassivation layer from the second passivation layer, and wherein theportion is in direct contact with the first passivation layer and thesecond passivation layer.
 11. The display pixel defined in claim 10further comprising: an organic layer, wherein the conductive layercomprises a transparent conductive layer that is deposited on theorganic layer.
 12. The display pixel defined in claim 11 furthercomprising: a display substrate; and transistor structures formed on thedisplay substrate, wherein the organic layer covers the transistorstructures and wherein the via structure contacts the transistorstructures.
 13. The display pixel defined in claim 12 wherein thetransistor structures include a channel structure formed from asemiconductor material selected from the group consisting of: amorphoussilicon, indium gallium zinc oxide, and polysilicon, wherein the gateelectrode is interposed between the channel structure and the organiclayer, wherein the via structure comprises a portion of the pixelelectrode structure that forms an electrical connection between thepixel electrode and the conductive layer.
 14. The display defined inclaim 1 wherein the via structure electrically couples the source-drainstructure, the capacitor electrode structure, and the pixel electrodestructure and wherein the via structure comprises first, second, andthird overlapping via portions.
 15. The display defined in claim 14,wherein the first overlapping via portion is formed from a conductivelayer that additionally forms the pixel electrode structure, wherein thesecond overlapping via portion is formed from the common electrodelayer, and wherein the third overlapping via portion is formed from thecapacitor electrode structure.
 16. The display defined in claim 15wherein the display further comprises: a common electrode structure inthe common electrode layer, wherein the common electrode structure doesnot contact the second overlapping via structure.
 17. A display,comprising: a pixel electrode structure; a capacitor electrode structurethat is electrically coupled to the pixel electrode structure; a commonelectrode layer that forms a parallel plate capacitance with thecapacitor electrode structure, wherein the common electrode layer has atransparent portion and wherein the transparent portion is interposedbetween the pixel electrode structure and the capacitor electrodestructure; and a source-drain structure that is electrically coupled tothe capacitor electrode structure and the pixel electrode structurethrough a via that overlaps the source-drain structure, wherein aportion of the pixel electrode structure extends through the via to forman electrical connection to the source-drain structure, and wherein thecapacitor electrode structure is interposed between the source-drainstructure and the pixel electrode structure.
 18. The display defined inclaim 17 wherein the capacitor electrode structure and the pixelelectrode structure form a storage capacitor with the common electrodestructure.
 19. The display defined in claim 18 wherein the pixelelectrode structure comprises first and second pixel fingers.
 20. Thedisplay defined in claim 19 wherein the capacitor electrode structureand the common electrode layer each overlap the first and second pixelfingers.